• Prokaryotes: cells which do not possess a nucleus 
• Eukaryotes: found in all multi-cellular organisms today 
• Has a distinct nucleus in which the DNA has combined with protein to form chromosomes surrounded by a protective nuclear envelope

The basic unit of living things. It can exist alone as a single, free, living plant or animal, or it can combine with other cells to form elaborate complex organisms, such as trees, horses, and people.

The cell is dynamic and carries all of the functions by which life is defined. It can grow, develop, reproduce, adapt, become influenced by outside stimuli, maintain a stable internal environment, and convert food into usable energy.

• Most animal cells are only 10 to 30 µm in diameter 
• Small cells have a proportionately larger surface through which they can absorb the substances they need. 
• A single nucleus can control the metabolic activity of a small cell better than a large one. 
• Large cells or cells that are very active have two or more nuclei.

• Structures found in all mammalian cells include the cell membrane, the cytoplasm, and the nucleus. 
• Everything inside the cell membrane other than the nucleus and genetic material is known as the cytoplasm. 
• Cytoplasm is composed of proteins, electrolytes, metabolites, a flexible cytoskeleton, and organelles. 

• Functions:  acts as a flexible, elastic barrier between the inner cytoplasm and the outside environment
• Governs the movement of atoms and molecules in and out of the cell 
• Consists primarily of protein and phospholipids 
• Also includes cholesterol , other lipids, and carbohydrates

• Lipid bilayer 
• composed of two layers of phospholipid molecules arranged so that the hydrophilic “heads” are on the outside and the hydrophobic fatty acid “tails” are on the inside
• Fluid mosaic 
• Proteins are suspended in the bilayer and move easily throughout the membrane to create a constantly changing pattern.

• Most lipid-soluble materials easily  pass through the membrane. 
• Water-soluble molecules do not readily pass through.
• The cell membrane contains structural and globular proteins: 
• • Integral proteins span the entire width of the membrane and may create channels through which other molecules can cross. 
  • Peripheral proteins are bound to the inside and outside surfaces of the cell membrane. 
• Glycocalyx: Phospholipids and the externally protruding ends of proteins on the outer layer are attached to sugar groups (glycoproteins and glycolipids).
• Enhances cell-to-cell adhesion and serves as a biological marker for cell recognition
• • Cell adhesion molecules (CAMs) 
  • Membrane receptors

• Extensions of the plasma membrane that extend into the extracellular space
• Composed of nine pairs of microtubules that encircle a central pair of microtubules
• Originate from a pair of centrioles called basal bodies
• Cilia and flagella grow outward from basal bodies and exert pressure on the plasma membrane

• Cilia occur in large numbers on the exposed surface of some cells.
• Move synchronously creating waves of motion that propel fluid, mucus, and debris across the cellular surface 

• Usually occur singly and are significantly longer than cilia 
• Attached to individual cells and propel the cell forward by undulating

• The fluid within the cell
• Viscous, semi-transparent
• Composed of dissolved electrolytes, amino acids, and simple sugars
• Proteins are suspended within and give it a thick, jellylike consistency
• Proteins are mostly enzymes 

• Three-dimensional frame for the cell
• Gives support and shape to the cell
• Enables cell motility
• Provides direction for metabolic activity
• Anchors the organelles
• Composed of:
• Microtubules
• Intermediate filaments
• Microfilaments 

• Membrane-bound structures within the cytoplasm that possess specialized cellular functions 
• The membranes of the organelles are similar in composition to those in the plasma membrane but do not have glycocalyx coatings.

• Produces most of the energy that fuels the cell 
• Enclosed by two membranes:
• outer one is smooth 
• inner one contains folds called cristae that increase the internal working area
• Matrix is liquid between cristae and composed of calcium ions, and substrates needed for metabolic reactions

• Series of flattened tubes stacked on one another and bent into a crescent shape 
• The walls of the ER are composed of a single lipid bilayer and are continuous with the membranes of the nucleus and Golgi apparatus.
• Rough ER has ribosomes on its surface and is involved in the production of protein
• Smooth ER is involved in the synthesis and storage of lipids.

• Composed of two globular subunits that contain protein and ribosomal RNA 
• Important site for protein synthesis
• Protein intended for intracellular use is manufactured on ribosomes that are distributed evenly and freely throughout the cytoskeleton. 
• Protein intended for use in the plasma membrane or meant for cellular export is synthesized on ribosomes attached to the endoplasmic reticulum.

• Composed of stacks of flattened, crescent-shaped tubes called cisternae
• Acts as a modification, packaging, and distribution center for molecules

• Lysosome: specialized vesicle formed by the Golgi apparatus 
• Contains hydrolytic enzymes enclosed in a single protective membrane 
• Functions to breakdown nutrient molecules into usable smaller units and to digest intracellular debris

• Membranous sacs containing enzymes found throughout the cell 
• Reproduce by pinching in half 
• Important in the detoxification of various molecules
• Assist in the removal of free radicals
• Two major types of enzymes: 

1. Peroxidases: assist in the conversion of free radicals to hydrogen peroxide
2. Catalases: reduce hydrogen peroxide to water

• Metabolic products or substances that the cell has engulfed 
• May have a single-layer membrane (e.g., secretory granules, vacuoles, and vesicles)
• May be non-membrane-bound (e.g., lipid droplets and fat globules)

• Small hollow cylinders composed of microtubules
• Found in pairs with their long axis perpendicular to one another 
• Visible during cell division 
• Help organize the spindle fibers during cell division 
• Form the bases of cilia and flagella

• Dark-staining, spherical or multisegmented body 
• Primary functions: maintain the hereditary information of the species and control cellular activities through protein synthesis
• Large cells are multinucleated
• Mature mammalian red blood cells are anucleated
• The anatomy of the nucleus is divided into the following four parts:

1. Nuclear envelope or membrane
2. Nucleoplasm: gel-like substance similar to cytoplasm
3. Chromatin
4. Nucleolus

Composed of two lipid bilayers

Outer layer is continuous with the ER and is studded with ribosomes 

Also consists of nuclear pores where the two layers of the nuclear envelope have fused to form a channel

• DNA and RNA are made up of chains of nucleotides. 
• Composed of three subunits: a nitrogenous base, a five-carbon sugar, and a phosphate group 
• DNA and RNA nucleotides are linked to form a “backbone” of alternating sugar and phosphate groups.
• DNA forms a double-stranded molecule called 
• the double helix.
• RNA is a single-stranded molecule that has no opposing strand. 
• The single strand of RNA is similar in structure to each of the strands found in DNA.

• Light or dark fibers in the nucleoplasm 
• Made up of DNA and histones
• Histones play an important role gene regulation
• A single strand of DNA winds around eight (8) histone molecules forming a granule called a nucleosome. 
• The nucleosomes are held together by short strands of DNA called linker DNA.

• Small, dark-staining spherical patches in the nucleus
• Not membrane bound 
• Located where ribosomal subunits are made
• These subunits are exported from the nucleus and are assembled in the cytoplasm to form functional ribosomes. 
• Nucleoli also contain the DNA that governs the synthesis of ribosomal RNA (rRNA).

• Intracellular fluid: inside the cell 
• Extracellular fluid: outside the cell
• Interstitial fluid: extracellular fluid specifically found in tissues

• Extracellular and intracellular fluid contains cations and anions.
• These ions are electrolytes.
• Acids and bases are also electrolytes.
• In sick or injured animals, the electrolyte concentrations and pH of intracellular and extracellular fluid can become abnormally high or low.

• The absorption of nutrients or excretion of waste may occur with or without the expenditure of energy by the cell. 
• Absorptive or excretory processes that require energy are considered active, whereas those that do not require energy are passive.

• Movement of molecules from an area of higher concentration to an area of lower concentration
• Various factors determine whether a molecule may pass through the cell membrane by passive diffusion:

1. Molecular size
2. Lipid solubility
3. Molecular charge

• Movement of molecules through the cell membrane with the assistance of an integral protein or carrier protein located in the bilayer  
• Requires no energy from the cell

• Passive movement of water through a semipermeable membrane into a solution where the water concentration is lower
• The force of water moving from one side of the membrane to the other is called the osmotic pressure.
• Osmosis occurs in the opposite direction of diffusion. 
• Unlike diffusion, the water, not solute, is moving. 
• Osmosis requires a selective membrane, whereas diffusion does not.

• Isotonic : Extracellular fluid has the same concentration of dissolved substances as intracellular fluid.
• Hypotonic: The cytoplasm of the cell is more concentrated than the extracellular fluid.
• Water flows into the cell and causes it to swell and possibly burst.
• Hypertonic: The extracellular fluid is more concentrated than the cytoplasm.
• Water shifts into the extracellular space, causing the cell to shrink and become shriveled.

• Based on a pressure gradient
• Higher pressure on one side of a membrane forces liquids through the membrane to the side with lower pressure
• Hydrostatic pressure

• Relies on a carrier protein with a specific binding site
• Does not require a concentration gradient
• Requires use of energy by the cell
• Example: sodium-potassium pump

• Substances to be exported are packaged in vesicles by the ER and Golgi body. 
• Vesicles move through the cytoplasm to the cell surface, fuse with the plasma membrane, and release their contents into the extracellular fluid.

Refers to changes in the distribution of the charged particles on either side of the cell membrane

Affected by the distribution of ions within and between intracellular and extracellular environments of all tissues.

• Chromosomes are a single piece of DNA coiled into a tight group. This structure contains genes, regulatory elements and nucleotide sequences
• Divided into autosomes and sex chromosomes
• These are all in the nucleus of the cell

• The life cycle of the cell has been divided into two major periods:

1. Interphase: The cell is growing, maturing, and differentiating. 
2. Mitotic phase: The cell is actively dividing.

• Period between cell divisions
• First part of interphase: growth 1 (G1) phase 
• Intensive metabolic activity and cellular growth 
• The cell doubles in size and the number of organelles also doubles.  
• Centrioles begin to replicate in preparation for cell division.
• Second part of interphase:  synthetic (S) phase 
• DNA replication

• Third part of interphase: growth 2 (G2) phase 
• Synthesis of enzymes and proteins necessary for cell division and continued growth of the cell
• Centrioles complete their replication.

• Chromatin uncoils  and the DNA unwraps and separates from histone proteins.
• Free nucleotides bond to one another in complementary pairs. 
• Primases attach a short chain of RNA to the DNA template strand (RNA primers).
• DNA Polymerase III places complementary nucleotides along the template strand and covalently links them together. 
• The lead strand, is made continuously; the second strand is made in segments 
• DNA ligase joins the segments.
• Telomeres, nucleoprotein caps, are placed on the ends of each DNA strand.
• DNA is wrapped around histone proteins forming chains of nucleosomes. 
• The identical DNA strands become chromatids, jointed together at a centromere. 

• Stages of mitosis:

1. Prophase
2. Metaphase
3. Anaphase
4. Telophase

• Cytokinesis: division of the cytoplasm

• Chromatin strands coil and condense to form chromosomes
• linked at a central kinetochore. 
• Spindle apparatus forms
• Nuclear envelope disintegrates

• Chromosomes line up in the center of the spindle.
• The centromere of each chromosome is attached to a spindle fiber.

• Chromatids are pulled apart by spindle fibers to form a duplicate set of chromosomes. 
• The cytoplasm constricts at the metaphyseal plate.

• Chromosomes begin to unravel at the poles of the cell.
• A nuclear envelope appears. 
• Cytokinesis marks the end of telophase.

• Contact inhibition
• Cyclins 
• Cyclin-dependent kinases (Cdks)

• Transcription: Genetic information in DNA is copied onto messenger RNA (mRNA).
• Translation: Complementary nucleotides pair with the mRNA to create the protein.

• RNA polymerase binds to a DNA molecule. 
• The double helix separates and causes the nitrogenous bases of a particular gene to be exposed.
• Complementary nucleotides are bound to the DNA, creating mRNA.

• Ribosomes bond to the mRNA strand.
• Transfer RNA (tRNA) brings amino acids (with the proper anticodons) to the ribosome.

• Involves the temporary or permanent inhibition of genes that may be active in other cells

• Errors in DNA replication
• Mutagen: anything that causes genetic mutation
• Viruses, ionizing radiation, and certain chemicals
• Spontaneous mutation